The present invention relates generally to the field of integrated circuits (ICs) and to methods of manufacturing integrated circuits. More particularly, the present invention relates to a method of manufacturing an integrated circuit including transistors with halo regions.
Integrated circuits (ICs), such as, ultra-large scale integrated (ULSI) circuits, can include as many as one million transistors or more. The ULSI circuit can include complementary metal oxide semiconductor (CMOS) field effect transistors (FETs) or MOSFETs. The transistors can include semiconductor gates disposed between drain and source regions. The drain and source regions are typically heavily doped with a P-type dopant (boron) or an N-type dopant (phosphorous).
The drain and source regions generally include a thin extension that is disposed partially underneath the gate to enhance the transistor performance. Shallow source and drain extensions help to achieve immunity to short-channel effects which degrade transistor performance for both N-channel and P-channel transistors. Short-channel effects can cause threshold voltage roll-off and drain-induced barrier-lowering. Thus, controlling short channel effects is important to assuring proper semiconductor operation.
Conventional IC fabrication techniques utilize a double implant process to form shallow source and drain extensions. According to the conventional process, the source and drain extensions are formed by providing a transistor gate structure without sidewall spacers on a top surface of a silicon substrate. The silicon substrate is doped on both sides of the gate structure via a conventional doping process, such as, a diffusion process or ion implantation process. Without the sidewall spacers, the doping process introduces dopants into a thin region (i.e., just below the top surface of the substrate) to form the drain and source extensions as well as to partially form the drain and source regions.
After the drain and source extensions are formed, silicon dioxide spacers, which abut lateral sides of the gate structure, are provided over the source and drain extensions. The substrate is doped a second time to form the deeper source and drain regions. The source and drain extensions are not further doped due to the blocking capability of the silicon dioxide spacers.
As transistors disposed on integrated circuits (ICs) become smaller, transistors with shallow and ultra-shallow source/drain extensions have become more difficult to manufacture. For example, smaller transistors should have ultra-shallow source and drain extensions with less than 30 nanometer (nm) junction depth. Forming source and drain extensions with junction depths of less than 30 nm is very difficult using conventional fabrication techniques. Conventional ion implantation and diffusion-doping techniques make transistors on the IC susceptible to short-channeling effects, which result in a dopant profile tail distribution that extends deep into the substrate. Also, conventional ion implantation techniques have difficulty maintaining shallow source and drain extensions because point defects generated in the bulk semiconductor substrate during ion implantation can cause the dopant to more easily diffuse (transient enhanced diffusion, TED). The diffusion often extends the source and drain extension vertically into the bulk semiconductor substrate. One technique utilizes shallow pocket regions which effectively suppress the short-channel effect (which degrades the robustness of the transistor to random process variations). Shallow pocket regions are provided in a conventional CMOS pocket implant process. The implant process is performed after the gate structure is fabricated and before the silicide layers are formed. The shallow pocket regions are not deeper than the source and the drain regions.
Another channel doping technique utilizes a two-dimensional doping implant, which is achieved by forming deep pocket implant regions, wherein the channel-doping profile in the lateral direction is non-uniform and the channel-doping profile in the vertical direction is a super-steep retrograded channel-doping profile. The two-dimensional channel-doping profile is critical to scaling (i.e., proportional operation for the ultra-small dimensions of the MOSFET). The deep pocket implant regions are conventionally formed after the extensions, drain and source regions and spacers are formed. The deep pocket results in a xe2x80x9chalo-likexe2x80x9d structure (e.g., halo regions). It is desirous to maintain the halo regions in a localized portion of the substrate.
As the critical dimensions of transistors continue to be reduced (e.g., to achieve a gate length of 50 mn and below), control of thermal budget in IC fabrication is very important. The term xe2x80x98thermal budgetxe2x80x99 refers to the temperature applied to the substrate during the fabrication process. The formation of ultra-shallow source/drain extensions and a super-localized halo profile for the halo regions is critical to control short-channel effects. In conventional CMOS processes, high temperature (e.g., greater than 1000xc2x0 C.) rapid thermal annealing (RTA) is used to activate the dopant in the source region, drain region, halo region, etc. However, the high temperature RTA can adversely affect the formation of the source, drain and halo regions.
With continually-shrinking MOSFET dimensions, high-k materials (i.e., materials having a high dielectric constant or k, such as, Al2O3, TiO2, ZrO2, etc.) can also be used as gate insulators. High-k materials tend to react with silicon at high temperatures. As such, the processing temperature has to be kept low (e.g.,  less than 800xc2x0 C.) if high-k materials are to be used as gate dielectrics. Accordingly, conventional CMOS processes cannot readily employ high-k gate dielectrics due to the adverse affects of the high temperature RTA.
Thus, there is a need for a manufacturing process for CMOS integrated circuits in which post-gate processing temperatures are lower such that high-k materials used as gate insulators do not react with silicon. Further, there is a need for a transistor fabrication process which uses a differential anneal strategy. Even further, there is a need for using an amorphous implant before the halo region, the shallow source/drain extensions and deep source/drain contact junctions are formed. Even further still, there is a need for an IC manufacturing process in which highly activated source/drain extensions, deep source/drain contact junctions and halo regions are created. Yet further, there is a need for an ultra-shallow source/drain extension and super localized halo region that can be economically fabricated.
An exemplary embodiment relates to a method of manufacturing a transistor. The method includes providing a gate structure, providing a self-amorphized halo implant, providing a shallow dopant implant, and forming a pair of spacers abutting the gate structure. The method also includes providing a self-amorphized deep source/drain dopant implant and annealing at a low temperature. The annealing at the low temperature activates dopants from the shallow extension dopant implant, the halo dopant implant, and the deep source/drain dopant implant via solid phase epitaxy.
Another exemplary embodiment relates to a process of forming a transistor on a substrate. The substrate includes a gate conductor. The process includes doping a halo region, forming a deep amorphous region, doping a shallow portion of the deep amorphous region, and doping deep source and drain regions. The method also includes recrystallizing the deep amorphous region. The shallow portion is doped for shallow source/drain extensions.
Yet another embodiment relates to a method of manufacturing a transistor on an ultra-large scale integrated circuit. The method includes steps of amorphizing a halo region in a substrate with a halo dopant implant, implanting a dopant into a shallow portion of the halo amorphous region of the substrate to form a source extension and a drain extension, implanting a dopant into a deep portion of the substrate to form a deep source and drain region, and recrystallizing the halo amorphous region.